The present invention generally relates to fiber optic illumination systems and, more particularly, to fiber optic illumination systems using a solid-state illumination device such as a light emitting diode.
Fiber optic illumination systems are designed to meet specific requirements that a standard illumination system cannot meet, for example, Illumination into volatile areas, into the human body, and into remote sites. Fiber optic illumination systems generally include a light source, a light guide device for transmitting the light from the light source to where it is needed, and an optical coupling of the light source to the light guide. Electric arc light is typically used as a high intensity light source. The light guide may be, for example, a fiber optic, fiber bundle, or wave-guide device.
The typical current method for optically coupling a light guide to the source is to provide a reflector or optic to focus the source light onto the target area of the light guide so that an illuminated area includes a spot of light falling on the face of the light guide. The spot size at the face of the light guide is a geometric function of the size of the source, i.e., there is positive magnification of the source light so that the spot size cannot be smaller than the size of the original light source. The geometric function depends on the angle of incidence of the cone of light that is impinging on the face of the light guide in such a way that, if the angle of incidence increases, the area illuminated decreases. In practice, for example, the spot size produced by an elliptical reflector is determined according to a geometrical equation, but leads to a spot size approximately four times bigger than the original light source. Such magnification requires a big light guide to couple all the source light energy, and the intensity of the light is spread over the larger spot area, lowering the light intensity per unit area.
One commonly used criterion for determining the light gathering power of an optical system is the concept of xe2x80x9cetenduexe2x80x9d. Etendue may be used to determine absolute values for the emitted (reflected or transmitted) energy, in order to control the overall energy balance in the optical system. Etendue may be defined as the product of radiant flux density and the area of a radiating or receiving surface. This product is a constant. So, if the angle of the incident cone increases, the area illuminated decreases. For a fiber optic, the highest angle of light that is accepted into the core of the fiber defines the numerical aperture (NA). For example, the numerical aperture can be determined by the differences in the indices of refraction of the core and cladding of the optical fiber and can be calculated using Snell""s law. An alternative way to calculate etendue for a fiber bundle is by multiplying the core area by the acceptance angle, i.e., the numerical aperture. The object of providing an efficient coupling is to capture all of the light rays. By matching the etendue of the light source to the etendue of the optical fiber, more of the light rays enter the fiber and stay in via total internal reflection (TIR). No system of external optics can increase the etendue of an optical system. This principle is called conservation of etendue. Thus, the most efficient optical coupling matches the etendue of the source to the etendue of the receiving light guide.
The current trend toward high intensity light emitting diode (LED) illumination has led to the ability to produce LEDs with efficacies near that of high intensity arc light sources. There has, therefore, arisen a need for the ability to couple a solid-state illumination device, such as an LED, to a fiber optic to support the features desired by fiber fed illumination systems. There has also arisen a need for the ability to provide the levels of intensity equal to that of other light sources. There are specific benefits in the use of narrow band illuminators, for example, ultra-violet (UV), blue, green, red, and near infrared (NIR). These narrow bands have been achieved through filtering of a standard white light source, which yielded low system efficiency as most of the light was thrown away as waste heat. The narrow band LED light sources, if efficiently coupled to fiber fed illumination systems, can give specific discrete bands required for special applications such as aircraft position and formation lighting or medical endoscopy.
As can be seen, there is a need for coupling a solid-state illumination device to a fiber optic to support the features desired by fiber fed illumination systems. Also, there is a need for coupling a solid-state illumination device to a fiber fed illumination system, which maximizes the coupling into the smallest feasible light guide. Moreover, there is a need for efficient coupling of narrow band LED light sources to fiber fed illumination systems.
The present invention provides coupling of a solid-state illumination device to a fiber optic to support the features desired by fiber fed illumination systems. The present invention also provides coupling of a solid-state illumination device to a fiber fed illumination system, which maximizes the coupling into the smallest feasible light guide. Moreover, the present invention provides efficient coupling of narrow band LED light sources to fiber fed illumination systems.
In one aspect of the present invention, a fiber fed illumination system includes a solid-state light source, which has a light emitting surface, a light guide, and a coupling assembly. In the coupling assembly the light guide is placed next to the light emitting surface of the solid-state light source, so that light from the solid-state light source is transmitted within the light guide.
In another aspect of the present invention, a fiber fed illumination system includes a solid-state light source having a light emitting surface, a light guide, and a coupling assembly. In the coupling assembly the light guide is placed next to the light emitting surface of the solid-state light source and the light guide is bonded to the light source. The coupling assembly further includes a plastic dome with a hole having the proper dimensions to accept the light guide. The plastic dome forms a cavity surrounding the light emitting surface, and the cavity is filled with an optical gel. Light from the solid-state light source is transmitted within the light guide.
In still another aspect of the present invention, a coupling assembly for optically coupling a light guide to a solid-state light source having a light emitting surface includes a plastic dome with a hole. The hole has proper dimensions to accept the light guide, and the plastic dome forms a cavity surrounding the light emitting surface. The cavity is filled with an optical gel, and the light guide is adjacent to the light emitting surface so that light from the solid-state light source is transmitted within the light guide.
In yet another aspect of the present invention, a fiber fed illumination system includes an LED light source having a light emitting surface; a light guide comprising a fiber optic; and a coupling assembly. In the coupling assembly, the light guide is placed next to the light emitting surface of the solid-state light source and the light guide is bonded to the light source. The coupling assembly further includes a plastic dome with a hole having the proper dimensions to accept the light guide. The plastic dome forms a cavity surrounding the light emitting surface and the cavity is filled with an optical gel. The size of the solid-state light source substantially matches the size of the light guide, and light from the solid-state light source is transmitted within the light guide.
In a further aspect of the present invention, a method of optically coupling a light guide to a solid-state light source includes steps of: providing a solid-state light source having a light emitting surface; substantially matching a size of the light guide to a size of the solid-state light source, whereby a smallest feasible light guide is used; placing the light guide next to the light emitting surface; and transmitting light from the solid-state light source through the light guide. The solid-state light source may have a concave shaped light emitting surface to provide maximized coupling by placing the light guide at the aperture of the concave shaped light emitting surface.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.